Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Amongst $He$,$Ne$,$Ar$ and $Kr$; $1 \ g$ of activated charcoal adsorbs more of $Kr$.
Reason $R$: The critical volume $V_c \left( cm^3 \ mol^{-1} \right)$ and critical pressure $P_c \left( atm \right)$ is highest for Krypton but the compressibility factor at critical point $Z_c$ is lowest for Krypton.
In the light of the above statements,choose the correct answer from the options given below.

• A
  $A$ is true but $R$ is false
• B
  $A$ is false but $R$ is true
• C
  Both $A$ and $R$ are true but $R$ is $NOT$ the correct explanation of $A$
• D
  Both $A$ and $R$ are true and $R$ is the correct explanation of $A$